The instant invention relates to control circuits for vehicle passenger safety restraints, such as air bags, comprising a firing path which includes two acceleration sensors whose acceleration-responsive switches are connected in series with an explosive squib.
Known air bag passenger restraint systems employ a control circuit wherein a power supply applies a voltage across a firing path which includes in series an explosive squib and two acceleration sensors having normally-open acceleration-responsive switches therein. The switch of each sensor is shunted by a resistor having a nominal resistance substantially greater than the internal resistance of the squib. Thus, a small current nominally flows through the firing path while the switches of the sensors remain in their normally-open positions. The closure of the sensors's switches in response to a collision or marked vehicle deceleration causes a significant rise in the current flowing through the squib, thereby "firing" the squib and triggering deployment of the air bag. See, e.g., U.S. Pat. No. 4,695,075, issued Sep. 22, 1987 to Kamiji et al.
Under the prior art, if the switch of either sensor fails in its closed position, or with a propensity to close, the prior art teaches the disabling of the entire control circuit to prevent the unintentional or premature triggering of the passenger restraint, once again placing the passengers at risk. See, e.g., U.S. Pat. No. 3,889,232, issued Jun. 10, 1975 to Bell, wherein the control circuit shuts down when one sensor closes without the corresponding closing of the other sensor.
Alternatively, in our U.S. Pat. No. 4,958,851 issued Sep. 25, 1990, we teach a reconfigurable air bag firing circuit whose firing path comprises two acceleration sensors connected in series with an explosive squib. The firing circuit further includes means for functionally removing the malfunctioning sensor from the firing path by closing or shunting the malfunctioning sensor, thereby providing continued protection of the vehicle passengers under the control of the remaining, still-operable sensor.
The instant invention is directed to an improved reconfigurable air bag firing circuit and an improved method of operating same.